As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a base layer, e.g. of paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of oxygen-barrier material, e.g. an aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a tube, which is fed vertically.
In order to complete the forming operations, the tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections; pillow packs are so obtained, which are then folded mechanically to form respective finished packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are then filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open the above packages, these are normally provided with a removable portion, which is partly detached by an opening device from the rest of the packaging material to free a pour opening through which to pour out the product.
The removable portion is formed on the packaging material prior to folding and sealing the packaging material to form the finished package.
The removable portion normally comprises a so-called “prelaminated” hole, i.e. a circular hole formed through the base layer only of the packaging material and covered, when the material is laminated, with the layers of heat-seal plastic material and barrier material, which adhere to one another at the hole.
Over the past few years, considerable research has been carried out within the industry to devise an effective, consistent method of opening prelaminated holes in such a manner as to achieve a clean cut about the edge of the pour-out opening, with no fraying impairing smooth pour-out of the food product.
Research has mainly been focused on devising various movements of the opening devices, when unsealing the packages, designed to cut the prelaminated hole as effectively as possible, and in particular on opening devices capable of unsealing the packages in one operation, i.e. severing the prelaminated hole and exposing the resulting opening in one user movement.
A first solution proposed is described, for example, in international Patent Application WO 95/05996, filed by the INTERNATIONAL PAPER Company, in which the opening device substantially comprises a frame, defining a spout and fitted about a removable portion of the package, a removable cap, screwed to the outside of the frame to close the spout, and a substantially tubular cylindrical cutter, screwed inside the frame, and which cooperates with the removable portion to detach it partly, i.e. with the exception of a small-angle flap, from the relative wall.
The cutter is activated by the cap by means of one-way ratchet-type transmission means, which are active when removing the cap from the frame. In the specific case described in the above international patent application, the cutter acts on the removable portion by means of an end edge parallel to the removable portion and having a number of teeth, all triangular and of the same height.
In actual use, the cutter moves spirally, with respect to the frame, from a raised rest position, in which the end teeth face the removable portion, into successive lowered cutting positions, in which the end teeth interact simultaneously with the removable portion.
Though successful in unsealing the packages in one operation, opening devices of the above type are unsatisfactory in that the teeth tend to “chew” the removable portion material, thus resulting in a jagged, frayed cut edge, which, at times, may divert flow of the food product as it is poured out. Moreover, the cut-off part of the removable portion remains hanging inside the package, and, in use, tends to at least partly clog the flow section of the spout, thus seriously interfering with outflow of the product.
To improve detachment of the removable portion from the rest of the packaging material, other solutions have been proposed, the most significant of which would appear to be those described in Patents EP-B-1513732 and EP-B-1509456, both filed by SIG Technology Ltd.
More specifically, in the first of the above solutions, the cutter is guided, as it penetrates the wall of the package, so that its travel comprises a first purely vertical translation portion, and a second purely horizontal rotation portion.
In the second solution, the travel of the cutter, when unsealing the package, comprises a first spiraling portion, and a second purely horizontal rotation portion.
Though improving cutting quality of the removable portion, the above solutions are still not altogether satisfactory in achieving a clean-cut edge with no fraying interfering with pour-out of the food product.
Finally, it should be pointed out that the above limitations are particularly noticeable when the removable portion of the package is made of particularly tough material, e.g. a barrier material covered with a polymer catalyzed with an organometal or metallocene. In which case, the removable portion tends to “stretch” rather than tear under the action of the cutter, thus resulting in an even more jagged, cut edge.
The Applicant has observed that effective, clean cutting of the removable portion does not depend solely on the type and movement of the opening device used, but also on the lamination quality of the hole formed through the base layer of the packaging material.
More specifically, the Applicant has observed that, the greater the area of the hole in the base layer to be laminated, the more difficult it is to achieve constant lamination pressure over the whole area, thus resulting in uneven thickness of the laminated polymer.
This therefore makes it difficult to achieve clean, consistent cutting of the removable portion using the many different types of currently existing opening devices.
Moreover, lamination of the hole in the base layer at higher and higher speed makes the quality of this operation very critical.